Signal transducer and activator of transcription 3 (Stat3) is an oncogene (Bromberg et al., 1999) and one of seven members of the STAT protein family, which are signaling intermediates that mediate the actions of many cytokines and growth factors. Stat3 is constitutively active in many different cancers including prostate, breast, lung, squamous cell carcinoma of the head and neck, multiple myeloma, colon cancer, hepatocellular carcinomas and large granular lymphocytic leukemia (Turkson and Jove 2000; Dong et al., 2003; Kortylewski et al., 2005; Lin et al., 2005; Tweardy and Redell 2005; Redell and Tweardy 2006). Furthermore, human tumor xenograft studies in mice have repeatedly demonstrated that inhibiting Stat3 results in decreased tumor growth and improved animal survival (Redell and Tweardy 2006) by inducing apoptosis in tumor cells, inhibiting angiogenesis (Kato et al., 2004) and enhancing anti-tumor immune-mediated cytotoxicity (Dunn et al., 2002; Kortylewski et al., 2005). Thus, Stat3 has been identified as a potentially high-yield target for drug development to treat many cancers (Yu and Jove 2004; Darnell 2005).
In contrast to Stat3, Stat1 is anti-oncogenic; it is a potent inhibitor of tumor growth and promoter of apoptosis (Bromberg et al., 1999). Also, because tumors from carcinogen-treated wild-type animals grow more rapidly when transplanted into the Stat1-deficient animals than they do in a wild-type host, Stat1 contributes to tumor surveillance (Kaplan et al., 1998). Consequently, a highly desirable goal in the development of drugs that target Stat3 is selectivity for Stat3 vs. Stat1, for example.
Drugs have been developed that selectively target Stat3 vs. Stat1 (Bhasin et al., 207; Jing et al., 2004; Coleman et al., 2005; Song et al., 2005; Schust et al., 2006; Siddiquee et al., 2007). However, determination of their selectivity was established empirically after their identification as Stat3 inhibitors and was not built into the screening process. There is a need in the art to provide novel compounds and methods for inhibiting Stat3 selectively.